Abstract Dietary intake is a powerful, modifiable factor that influences cancer risk. Unfortunately, most adults in the U.S. find it difficult to adhere to dietary guidelines for cancer prevention. One promising pathway for improving dietary adherence is to target grocery shopping habits, i.e., foods purchased for consumption at home. Two- thirds of daily food intake is sourced from or eaten in the home, so improving the quality of the home food environment should improve overall diet quality. When healthy foods are purchased and unhealthy foods are not, minimal self-control is needed to make healthy eating choices in the home. At the point of purchase, it is difficult to resist the temptation of palatable foods, but interventions might facilitate healthy choices by a) promoting dietary goal salience in real-time while grocery shopping, b) enhancing motivation to make and sustain changes to the diet, and c) increasing household support and accountability for healthy food purchasing. At this stage of research, methodical testing of intervention components that can change food purchase behaviors is needed, in order to craft an mHealth intervention package that is feasible, acceptable, and optimized for efficacy and scalability. The proposed study will enroll adults (N = 64) who have low adherence to cancer prevention dietary recommendations. All participants will attend a 3-hour nutrition education workshop. For 6 months following the workshop, all participants will receive text notifications that provide tailored reminders and recommendations for food purchasing. The study will use a factorial design to experimentally test four additional intervention components and examine their feasibility, acceptability, and effect on food purchases and dietary intake at 3 and 6 months. (Each component is randomly assigned to be activated for 50% of participants.) The four components to be tested are: 1) Location-triggered text notifications: Reminders and recommendations for food purchases are delivered ?just-in-time,? when arriving at grocery shopping locations, to enhance goal salience. 2) Reflections on the benefits of change: To enhance motivation, content is added to messages to encourage reflection on the anticipated benefits of healthy eating. 3) Coach monitoring: Food purchases are automatically monitored by a coach (through a system that collects item-level store data) who sends personalized post-purchase messages designed to enhance supportive accountability and thus motivation. 4) Household text: Other adults in the household receive messages designed to elicit support for healthy food purchasing and provide another source of supportive accountability. The preliminary aim of the study is to assess feasibility and acceptability of the intervention components. The primary aim of the study is to quantify the effect of each intervention component, individually and in combination, on grocery store food purchases (objectively assessed with store data), and dietary intake (assessed with 24-hour food recalls). Mediation analyses also will be conducted. The overarching goal of this project is to optimize this mHealth intervention, which can be tested in the future in a fully powered clinical trial.